As benzopyran derivatives, 4-acylaminobenzopyran derivatives exemplified by Cromakalim have been known (Japanese Patent Laid-open No. Sho 58-67683). These 4-acylaminobenzopyran derivatives exemplified by Cromakalim are known to open ATP sensitive K+ channel so as to be effective for the treatment of hypertension and asthma, but there has not been any mention as to the treatment of arrhythmia based on the prolongation effect on the refractory period.
At present, conventional anti-arrhythmic agents having the prolongation effect on the refractory period as a main mechanism (such as Class I drugs of anti-arrhythmic agent classification according to Vaughan Williams, or d-sotalol or dofetilide belonging to Class III) have the therapeutic problems in inducing highly dangerous arrhythmia leading to the sudden death from such as torsades de pointes among others due to prolongation of action potential in ventricular muscle correlated to the prolongation effect on the refractory period. Thus, treating agents with less adverse effect have been highly desired.